. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. HUNTINGTON AND GOLDTHWAIT: THE HURRICANE FAULT. 253 far enough to produce the young and vigorous topography of II. The hard Carboniferous strata, A', have been but little affected except in the immediate river valleys, where deep narrow canyons, /' and H', have been cut with very precipitous sides. The overlying soft strata, B', have been entirely stripped off except where they are buried under lava and form mesas, G', or where they are protected by the Shinarump, C. In the same way the Painted Desert strata,
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. HUNTINGTON AND GOLDTHWAIT: THE HURRICANE FAULT. 253 far enough to produce the young and vigorous topography of II. The hard Carboniferous strata, A', have been but little affected except in the immediate river valleys, where deep narrow canyons, /' and H', have been cut with very precipitous sides. The overlying soft strata, B', have been entirely stripped off except where they are buried under lava and form mesas, G', or where they are protected by the Shinarump, C. In the same way the Painted Desert strata, Z)', have been removed, and the overlying hard Kanab, E', forms cliffs. To-day these cliffs are rapidly retreating but erelong talus from the upper hard layers will so cloak the lower soft layers that the slopes will become more moderate and the retreat of the cliffs much slower. I E -, c .—1_ ex T5 B M A - 1. Figure 12. North-south sections to show the work of the present cycle. The best example of the stripping of soft strata is the great Carbon- iferous platform, in which is cut the canyon of the Colorado. Here, over an area of hundreds or even thousands of square miles, a few hun- dred feet of Moencopie shales have been stripped off, as is shown by the unconsumed patches remaining here and there, and by the larger masses preserved under lava caps. Although the most notable feature of the cutting of canyons is the Grand canyon, others, such as that of the Vir- gin river, are worthy of mention. An interesting case is that of Ash creek, which now flows in a shallow canyon at the foot of the Hurricane fault north of Toquerville. As this is part of the downthrown block, the amount of cutting has naturally been less than in corresponding cases on the other side of the fault. The notable feature, however, is that a short distance west of the present canyon is another of about the same size which is now dry and lies on the crest of an arched sheet of basalt. Please note that the
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